6x12 cnc plasma table questions

[TRed]

I'm close to ordering parts for a 6 x 12 table. One issue I have is keeping the gantry weight down. I may add a router at some point so I may be over building. I plan to use candcnc https://www.candcnc.com/store-home/f...-servo-bundle/

I'm going to be using 3 x 4 x 3/16" for the gantry. Due to the length I chose 4" vertical dimension. Using this it looks like I will be a little over the 125lb limit for the gantry. Should I be worried?

Thanks,
Tim

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[NIC 77]

I'm close to ordering parts for a 6 x 12 table. One issue I have is keeping the gantry weight down. I may add a router at some point so I may be over building. I plan to use candcnc https://www.candcnc.com/store-home/f...-servo-bundle/

I'm going to be using 3 x 4 x 3/16" for the gantry. Due to the length I chose 4" vertical dimension. Using this it looks like I will be a little over the 125lb limit for the gantry. Should I be worried?

Thanks,
Tim

Where are you in Canada. I'm in southwestern ontario. I have a large router that would be perfect for a plasma conversion. Alot less $$ and easier to buy from me and fix it up as a plasma than to build from scratch. If you're in the neighborhood, send me a PM.

As to your question for a gantry that size, 125lbs is really not much. Fine for a plasma, but on the light side for a router. No, I wouldn't worry about it.

I clicked on the link. They don't give any relevant info that I could find. Not even how many watts the servos are. Not even the gear ratio of the reducers is given!

Really, the long answer to your question is that I would need to see the torque vs speed graph for the servos, the inertia of the motor, the gear ratio, the inertia of the reducer, the effective radius of the pinion, (assuming rack and pinion), and the all up weight of the gantry including everything that moves back and forth including motors, Y axis, Z axis, everything attached to it. And then I would need to know your goals for speed and acceleration.

The short answer is don't worry about it.

I've heard good things about candcnc torch height controls, but I have to wonder if this servo system is overkill. Nema 34's should be fine with a 2:1 or 3:1 belt driven gear reduction even for a gantry 3 times your weight.

[NIC 77]

Sorry, I thought it said you were from Canada, I must have got my threads mixed up.

[Torchhead]

The servo gearboxes on that kit are rated for 115 lbs for a direct drive to a 1" pinion from the gearhead. What does that mean? Its based on what we have found as minimum acceptable acceleration rates of at least 35 IPS/sec up to at least 250 IPM cutting speeds. Because servos have virtually flat torque curves over the full RPM you can proabably extend those speeds up to 350 or higher. So the basic physics formula is A - F/M (acce = Force/mass) Y0u have to convert rotary torque to linear force (ft-lbs) and the mass to ERGs (weight/32) to get Ft/sec accel .
The gantry weights we recommend are based on experience and math. If you are concerned about not having enough force to keep the acceleration up full spec you can add in a mild belt reduction (1.5 :1 ) after the gearbox and gain about 50% more torque and take the weigh limit up to over 165 lbs. It reduces your upper IPM from about 1000 IPM tops to about 700 IPM tops .

One other option is to look at the stepper version with the 620 motors and 3:1 gear reduction units (avialble from 3rd party sources) and upsize the two gantry motors to the 980's and you are then there to drive a 150 to 160 lb gantry at cutting speeds with more that 35 IPS/sec acceleration rates . The 980's are 34 size motors so mountings and shaft size are larger .

Our numbers are based on real world testing and extended cutting . It's one thing to talk theory and another to talk experience. The engineering approach you use for plasma is different than router .

TOMcaudle
CandCNC

[TRed]

Would a 3 x 3 8020 beam be strong enough for a gantry aprox 84' long? It would lighten the gantry wt considerably.

I have decided to forget about the idea of a router also. I now see plasma and routing have different requirements.